Such drive systems can be found in all conventional vehicles. All vehicles have, as loads, at least those components which are required for the movement of the vehicle, in particular the driven wheels of a vehicle. A further conventional load in vehicles is the alternator, by means of which electrical energy is provided for operating a vehicle power supply system with electrical loads. In particular in the sector of tracked vehicles, hydrostatic drives are also often used in which the drive machine is used in order to drive one or more hydraulic pumps which in turn make available, for hydraulic motors, the pressure required for the progressive movement of the relevant vehicle.
In many vehicles today, a large number of loads are connected to the drive machine such that they cannot be detached mechanically. A consequence of this, which is regarded as disadvantageous, is the fact that these loads, starting directly when the drive machine is started, have a power consumption which impairs the starting behavior of the drive machine. This can easily result, in particular in the case of the abovementioned tracked vehicles with a hydrostatic drive, in a power consumption of the loads, on starting, which exceeds the output of mechanical power by the drive machine and thus results in the drive machine stalling. The problem is also heightened if the loads are those which have an initial power consumption on starting which is higher than the power consumption during normal operation.
In order to be able to provide the required power in the starting phase, it is known to decouple loads mechanically from the output drive of the drive machine, for example by disengaging the clutch in the case of a passenger vehicle. However, this method is relatively complex in design and is not favorable in economic terms. Depending on the type of load, such a mechanical separation also represents a source of danger, for example when disengaging feed pumps of a hydraulic drive system. If the mechanical coupling in such a system fails and, as a result of this, the operating pressure in the closed drive circuit cannot be maintained, it is not, for example, easily possible to brake the hydraulic motor counter to a torque which is brought about externally and acts on the hydraulic motor.